1. Field of the Invention
This invention relates to an improvement in a ceramic substrate for use in a semiconductor package for storing semiconductor elements, and more specifically, to a ceramic substrate in which chipping of its end portions due to collision with another substrate is prevented during transfer and conveyance of the substrate or the semiconductor package.
2. Description of the Prior Art
Conventional ceramic substrates used for semiconductor packages are provided with various measures taken to prevent chipping upon their collision with each other.
For example, Japanese Laid-Open Utility Model Publication No. 49444/1983 discloses a ceramic substrate having a planar portion with a size A of 2 to 8 mm located centrally at the end surface of a short side of the substrate, taper surfaces each having a size C of 0.1 to 0.5 mm smaller than size B extending from both side lines of the planar portion toward both side ends, and an arc R having a size D of 0.3 to 1.5 mm at a cross position between the end surface of a long side of the substrate and the taper surface, as shown in FIG. 5. When such conventional ceramic substrates are transferred in a container having a large clearance, or moved through a transfer passage having a large clearance, the ceramic substrates rock. As a result, the arcuate portion R frequently collides with other ceramic substrates and undergo chipping. A notch N for clearly showing the position of taking out lead terminals from semiconductor elements stored in the substrates is usually provided in the planar portion formed approximately at the center of the end surface of the short side, and minute wavings occur in the neighborhood of the notch N as a natural consequence of substrate production. Hence, in the event of collision between ceramic substrates, the stresses of collision are concentrated on the neighborhood of the notch portion N and may result in chipping of the notch portion N.
Japanese Laid-Open Patent Publication No. 119748/1984 discloses as shown in FIG. 6 that a plurality of wavy portions Y having nearly the same wave height are formed on the end surface of a short side of a ceramic substrate used for a semiconductor package. However, in relation to the fact that in the ceramic substrate, wavy convex portions Y and concave portions Z are formed with nearly the same amplitude (wave height) with respect to the center line Z, this ceramic substrate has the following defects. Specifically, in a production line for semiconductor packages or semiconductor devices, discrimination of the directions of ceramic substrates or packages using them or the regulation of their positions are effected at the central part of the short side of the substrates. Since the increasing of the amplitude exceeds the allowable limit of the direction discrimination or position regulation, the wave height of the wavy portions Y has to be maintained small. Accordingly, in the transfer of ceramic substrates in which rocking is liable to occur, the corner portions may also collide to undergo chipping.